Sanitation and water management

Public Health Significance of Urban Pests Mosquitoes 363 362 1. Flooding of subfloor crawl spaces, cel- lars and basements in houses or apart- ment buildings plays an important role in the establishment of breeding sites for the northern house mosquito. To prevent such breeding sites, it is important that effective drainage and water-proofing measures be implemented, that residual water be pumped out and that potentially floodable space be filled with gravel, up to the highest level of the water table. 2. For cesspits and cisterns, mosquito nets should be installed in aeration gaps, to ensure that covers do not leak. For septic tanks, open discharge should not be allo- wed. Instead an underground purifica- tion bed should be installed; once it is lin- ked to a sewer system, the old pit should be filled or destroyed. Also, wells, wate- ring and leisure pools, rainwater tanks, swimming pools not in use, construction site excavations, potted plants with sau- cers, cemetery flower vases and diverse containers must not be prone to mosquito development. To avoid it, any water reservoirs should be emptied every 10 days or be covered with mosquito nets. Moreover, all receptacles not in use should be eliminated. Furthermore, goldfish can be introduced in leisure ponds. Finally, containers exposed to the weather should be emp- tied, turned over or discarded. 3. For rainwater channels, all obstacles to the flow of water should be removed. 4. Water treatment plants working on a part time basis can create problems, if they are too big for the amount of water to be treated. Also, abandoned plants that still retain rain- water can create problems. 5. Wastewater treatment ponds should be clear of rooted vegetation, and the water height should be maintained at more than 80 cm. Ponds that use vegetation as a purification measure should be sufficient in number, so as to allow for more than one month of total dryness a year in winter, to prevent Coquillettidia spp. from becoming established. Also, embankments must be covered with cement or a geotextile fabric, and ponds must be designed in a manner that avoids zones with stagnant waters. Fig. 11.2. Some sanitary measures that can considerably reduce mosquito problems Note. The numbers encircled in red correspond to the following areas where sanitary measures can be used: 1. flooding of subfloor crawl spaces, cellars and basements in houses or apart- ments; 2. cesspits and cisterns, wells, watering and leisure pools, rainwater tanks, swimming pools not in use, construction site excavations, potted plants with saucers, cemetery flower vase and diverse containers; 3. rainwater channels; 4. water treatment plants; and 5. wastewater treatment ponds. Source: Schaffner 2003. Integrated control aims to synergize a range of measures intended to reduce and control the nuisance or the vectorial transmission. It aims to reduce the density and the longevity of vector insects by adapting measures to the environmental and epidemiological local conditions. The monitoring and reappraisal of field conditions allow permanent read- justments of these measures, with the objective of better effectiveness and less damage to the environment and human health. Integrated control proposes: • sanitation, environmental modification measures and biological control, to reduce the development of vectors and to maintain their density under a minimum threshold; • larviciding with chemical or biochemical insecticides, for a rapid reduction of the like- lihood of mosquito proliferation; • residual adulticiding, to reduce the longevity of vectors and to stop the cycles of trans- mission; and • passive protection measures, to reduce host–vector contacts. Guidelines for surveillance, prevention and control plans are already developed in seve- ral countries for managing the risk of WNV CDC, 2003; CDHSMVCACUC, 2004; SSSQ, 2006; MSSMAPMMEDD, 2005.

11.8.1. Sanitation and water management

Sanitation and water management, such as source reduction, are key to any solution of a mosquito problem. Depending on the species, culicid mosquitoes develop in many dif- ferent types of natural and artificial waters. Mosquito larvae can be found in clean and polluted, fresh and brackish, and stagnant or slow-flowing waters, such as marshes. They can also be found in river deltas, rice fields, swamps, tidal floodwaters, lakes, puddles, pools, ponds, tree holes, rock holes and creeks, as well as in gutters, flowerpots, tin cans, buckets, dishes, tyres, pits and cellars. Source reduction is therefore the only long-term solution to mosquito infestation, espe- cially in urban areas Schaffner, 2003. This method requires modification of aquatic habi- tats – for example, some natural habitats could be modified to reduce the production of mosquitoes by a relative stabilization of the water level. Preventing, or at least identi- fying, stagnant waters is crucial in artificial areas that may provide breeding sites for the northern house mosquito, the Asian tiger mosquito, or the yellow fever mosquito Fig.11.2. This can be accomplished by avoiding stagnation in sewers, draining stagnant water from subfloor crawl spaces or closing air gaps with mosquito nets, covering tyre stocks or storing tyres in warehouses, removing containers that hold water or at least regularly replacing the water Fig. 11.3a–c. As Fig. 11.2 illustrates, there are five sanitary measures that can reduce mosquito pro- blems considerably. Public Health Significance of Urban Pests Mosquitoes 365 364 cal temephos, biochemical such as Bacillus thuringiensis var. israeliensis and Bacillus sphaericus or IGR such as diflubenzuron and methoprene, depending on compliance with local regulations. Biochemicals and growth regulators have the advantage of being more specific, whereas chemicals are less expensive and easier to use, especially for very large habitats WHO, 1996; Chavasse Yap, 1997.

11.8.3. Adulticiding